This application is to request support for a Keystone Symposia meeting entitled "Pathogenesis and Immune Regulation in Helminth Infections", organized by Richard M. Maizels and Maria Yazdanbakhsh, which will be held in Tahoe City, California from February 1 - 5, 2009. The immunology of parasitic helminths is now attracting intense interest, due to the exciting and intricate relationship between immunity and pathogenesis, the proposed significance of regulatory immune controls in modulating both infection and disease, including allergies and autoimmunity, and the application of new molecular tools to the field situation. Currently, research aims to trace how helminths manipulate host immune cell populations, identify molecular mediators and receptor pathways involved in the host-pathogen dialogue, and design new interventions for control of infection in both human and animal contexts. This meeting will bring together scientists from many different countries (particularly those highly prevalent for helminth diseases), bridging from reductionist model systems, which offer proof of principle, to the epidemiological scale in which major insights are gained from natural infection settings. New questions from field and laboratory research will be generated, promoting the integration of different strands of inquiry and paving the way for new strategies for disease control. Over one-fourth of the world's population is infected with helminth parasites, making the translation of scientific understanding to new field applications of immense global importance. This meeting will provide a continuum of helminth disease research: from the seminal studies on immune reactivity in infected human populations, through the analytical dissection of immunological components in both humans and rodents, to the "big picture" discussion of human diseases and how they may be controlled in the future.